The regulation of parathyroid hormone (PTH) secretion by calcium and other secretagogues is thought to involve cyclic AMP (cAMP)-dependent as well as cAMP-independent pathways. Calmodulin is a polyfunctional, intracellular calcium "receptor" which may regulate and integrate cellular calcium homeostasis and cAMP metabolism. It is thought to carry out these functions by causing a calcium-dependent activation of a variety of enzymes, whose functions include cAMP synthesis and degradation, transmembrane calcium transport, protein phosphorylation, and prostaglandin biosynthesis. We have recently demonstrated the presence of calmodulin and calmodulin-activated phosphodiesterase in dispersed bovine parathyroid cells. In view of its potential importance in this tissue, we plan to localize calmodulin within the parathyroid cell and to examine these cells for calmodulin-regulated enzymes with possible relevance to the control of hormonal secretion. Specific goals of the project are as follows: (1) We will employ immunofluorescence with an anticalmodulin antiserum to define the location of calmodulin within the cell and to examine the effects of various secretagogues on its distribution. (2) We will define and characterize within parathyroid cells (Ca++-Mg++)-ATPase, an enzyme though to regulate cellular calcium transport. ATPase activity will be measured in membrane preparations from parathyroid cells and the effects of calcium and calmodulin on enzymatic activity will be determined. (3) We will examine the parathyroid for calmodulin-regulated, myosin light chain kinase and other calcium-regulated protein kinases by measuring the phosphorylation of exogenous and endogenous substrates for these enzymes. (4) We will employ radioimmunoassay to determine the effects of calcium on the biosynthesis by parathyroid tissue of prostaglandins, agents which have both stimulatory and inhibitory effects on this cell type. The definitive localization and identification of specific functions for this protein in the parathyroid cell could provide new avenues for investigating the roles of cytosolic calcium and cellular cAMP in regulating PTH release. Moreover, studies of alterations in the distribution and action of calmodulin in pathologic human parathyroid tissue might provide clues to the basis for the abnormal calcium-regulated PTH release in primary hyperparathyroidism.